1. Field of the Invention
The present invention relates to an image taking system including an image sensor that is configured to take an image of an object, and also to an electronic-circuit-component mounting machine including the image taking system.
2. Discussion of Related Art
There is known an image sensor including a plurality of unit cells formed in an image taking area of the sensor. Each of the unit cells is configured to perform a photoelectric conversion, namely, convert an optical image to an electric signal. JP2008-112931A discloses an image taking system including unit cells each having a CMOS image sensor that is constituted by CMOS (complementary metal oxide semiconductor). This image taking system is disposed in an electronic-circuit-component mounting machine, and is configured to take an image of an electronic circuit component (held by a suction nozzle) from under the electronic circuit component. In this image taking system, a sensitivity of a part of the image taking area is adjusted such that each of the image of the electric circuit component and its background image is taken with an even brightness. Upon adjustment of the sensitivity, the image of the electronic circuit component held by the suction nozzle is taken, and the image of the electronic circuit component and the background image are shown on a monitor display. An operator visually confirms the image of the electronic circuit component and the background image through the monitor display, and selects a region including a dark portion, i.e., a region in which the sensitivity is to be corrected. The monitor display indicates an image brightness in each unit area. When the operator selects the region in which the sensitivity is required to be adjusted, namely, in which the brightness is lower than a reference value, a sensitivity adjustment table is prepared for adjusting the sensitivity of each of unit areas included in the selected region, such that the brightness of the selected region becomes substantially equal to the reference value. When the image of the electronic circuit component is to be taken after initiation of an operation for mounting the component onto a circuit board, a sensitivity adjustment value is read from the prepared sensitivity adjustment table, and the image of the electronic circuit component is taken based on the adjusted sensitivity, by the CMOS image sensors, so that it is possible to obtain the image without any portion in which the brightness is smaller than the reference value, and accordingly to accurately obtain information such as a position of the electronic circuit component relative to the circuit board.
JP-2006-74114A discloses a digital camera including a CCD image sensor in which each unit cell is constituted by CCD (charge coupled device). In this digital camera, a plurality of ROI (regions of interest) are set within an image taking area, and an image data is subjected to predetermined processings that are performed in accordance with a desired image-quality level that is set for each of the plurality of ROI. The image data is converted through the processings, and then is shown in a display device. As the predetermined processing, for example, a filtering, a color conversion and a brightness conversion are performed. Specifically described, the filtering is performed by a filtering coefficient that varies depending on the desired image-quality level, such that a region of the image corresponding to each ROI (in which the desired image-quality level is relatively high) is made relatively clear. The color conversion and brightness conversion are performed by a color-conversion coefficient and a brightness-conversion coefficient, respectively, which vary depending on the desired image-quality level, such that the region of the image corresponding to each ROI (in which the desired image-quality level is high) is given color and brightness that are relatively close to those of an original image.